Process for reclaiming cellulose ester material



Patented Dec. 28, 1943 PROCESS FOR RECLAIMING CELLULOSE ESTER MATERIAL Charles R. Fordyce and Joseph Gail Stampfli,

Rochester, N. Y., assignors to Eastman Kodak 7. Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application January 8,1942,

Serial No. 426,054 7 i 8 Claims.

This invention relates to the separation of a thin layer of a hydrolyzed cellulose ester from a thicker cellulose ester layer to which it adheres, the thin layer being of a lower acyl content than the thicker layer, by treating with a dilute aqueous solution of an alkali metal permanganate and a strong mineral acid at a temperature of at least 150 F.

Ordinarily, photographic film consists of a base of a cellulose ester, one or more subbing layers, and a photosensitive emulsion thereon. Our invention relates to photographic film in which the base is an organic acid ester of cellulose. One or more subbing layers are applied thereover, followed by a gelatin coating or coatings, at least one of which contains photosensitive material. In the recovery of film scrap, the gelatin material is removed first, usually by means of hot water which softens or dissolves the gelatin and thereby loosens it from the cellulose ester material. The resulting material will then ordinarily consist of a base of a lower fatty acid ester of cellulose and one or more subbing layers of a lower fatty acid ester of cellulose which has been hydrolyzed to a greater extent than the film base ester. Our process is particularly applicable to cellulose ester materials primarily composed of a lower fatty acid ester of cellulose and having on one or both surfaces a thin layer of a similar type of cellulose ester but containing) at least, per cent less acyl than the film H retofore, permanganates such as potassium permanganate have been employed in film scrap recovery processes, but usually those processes were merely concerned with removing the color or dye from the film. In those cases, the permanganate served as an oxidizing agent and could well be replaced b some other oxidizing agent such as hydrogen peroxide or some kind of a chlorine compound.

One object of our invention is to provide a process of recovering film base cellulose esters in which the use of chlorine compounds is unnecessary. Another object of our invention is to provide an inexpensive, but effective, method of removing cellulose ester subbing layers from cellulose ester sheeting. Other objects will appear herein.

We have found that cellulose ester sheeting made up of a thin and a thick layer of cellulose esters, thelatter being less hydrolyzed than the former when treated after being chopped into small particles with a dilute solution of acidified permanganate in water at a temperature of at least F., effectively loosens or removes the thin cellulose ester layer from the cellulose ester sheeting which is to be recovered.

Our process involves the treatment of cellulose esters such as cellulose acetate, cellulose acetate propionate, or cellulose acetate butyrate, or simple esters of the lower fatty acids in which a thin layer of one or a mixture of these esters is present therein; the acyl content of the ester of the thin layer being at least 5 per cent less than that of the base of the sheeting. Ordinaril there would be employed esters of not more than 10 per cent difference in acyl between the thin layer and the film base, or thick layer, because of the difiiculty of otherwise obtaining adhesion. To illustrate, if the film base is composed of a cellulose acetate having an acetyl content of 40 per cent, it is usually desirable that the subbing layer have an acetyl content of more than 30 per cent. If however good adhesion should be attained between esters having more than 10% difference in acetyl, our process would also be applicable to reclaiming the scrap of the product obtained, Any thin layer of cellulose acetate or some other lower fatty acid ester of cellulose, for that matter, which has a more than 35 per cent acyl content cannot be satisfactorily treated by our invention, when the film base ester has an acyl content of no more than 40% or in other words there should be a span of at least 5% in acetyl contents.

The treating liquor .is an aqueous solution of potassium (or other alkali metal)v permanganate, and for economys sake, contains between .25 and 2 p'e-r 'cent of pern'ian'g'anate;v Obviously, if economy is not a consideration, a concentration iof permanganate up to5 percent, or even more. can very well be employed. Itis preferable that the amount-of acid 'whicliis employed to acidify the treatingliquor be atleast twice that of the permanganate, figured in terms of molecular equivalents. It is only necessary that sumcient acid be employed to give a strong acid solution. The acid which is employed should be an inert strong acid, preferably mineral. Some of the acids which are useful are sulfuric acid, phosphoric acid, nitric acid, benzene sulfonic acid, or the like. As sulfuric acid has been found to be the best and the cheapest for this purpose, it is preferable to use sulfuric acid when removing subbing layers in accordance with our in vention. As the presence of chlorides is usually undesirable, avoidance of the use of chlorinecontaining acidsis recommended.

We have found that ordinarily the subbing layer the temperature used, but also on the ease with.

which the subbing layer is loosened from the cellulose ester sheeting to which it isattachedl, For instance, a cellulose acetate having an acet'ylf content of 30 per cent is more susceptible to penetration by the treating liquidand'hence, is more. easily removed in accordance with. our invention than a cellulose acetate having an acetyl content of 35 per cent. It is preferable that a temperature be employed which will bring about the reuntreated film scrap, which was incompletely dismoval of the subbing layer from'the film base-in at least one hour and preferably less. Although it is desirable to operate at a temperature between 150 F. and the boiling point of water, the tem perature may be raised above this: range without detrimentally afiecting the operation of the process. Obviously, if the temperature is above the boiling point of the water, it is desirable either to operate in an enclosed vessel or under conditions whereby the liquid, after boiling oif, is returned to the vessel or is replaced by a fresh addition of water. No advantage has been found,

however, in operating; under pressure. After the 5 subbing layer has beenv treated until it becomes water soluble or, at least, water susceptible, the scrap is washed" to remove this material leaving only the film base which ordinarily consists of the cellulose ester and plasticizer. The film base sorecovered when dissolved in a solvent. forms a clear solution which is suitable forreuse in making sheeting for theproduction of'filmbase or any other purpose.

Ordinarily, in treating the film scrap with the permanganate solution, especially with the lower concentrations of permanganate, the disappearanceiof the purple color signifies the end of the treatment. It is preferred to then wash the scrap with hot acid sodium sulfite solution, therebyremoving the manganese dioxide which is formed by the process. Although there is no critical limitation of the amount of treating liquid'to be employed with a given amount of film scrap, we have found that20parts of'liquid to one part ofz'scrap gives a satisfactory condition of treatment and allows thorough mixing of the scrap; especially in finely chopped condition, .withthe permanganate solution.

. The following examples illustratethensefulness of our process.

Example. I.

40- grams; of. chopped safety film, scrap containing bluedye andfromwhichthe gelatin emulsiont has. been; removed was stirred and heated to a temperature between 180 and 212 F. in about 800 cc. of an aqueous solution containing 1 percent KMnO4 and 2 per cent of. HNOs. The

base, from which the film was made was cellulose acetate butyrate having approximately 30 per centacetyl and 17 per centbutyry1 content. The subbing layer thereonwas a cellulose acetate propionate containing about 24 per cent acetyl and 15.5 per cent propionyl. The elevated temperature was maintained until the purple permanganate color was: discharged. The liquid was drained off and the mass was stirred a short time with 800 cc. of. ahot acidic 1 per cent solution solved, and deep blue in color.

A practical test to determine whether or not the thin. cellulose ester layer has been completely removed; is to prepare a viscous solution of the material in a solvent or solvent mixture which will readily dissolve the heavy film but is not a solvent for the thin coating. The untreated films, or those in which the thin layer has not been completely removed, give, under this test, solutions containing numerous particles of undissolved material, while products from which the thin coatings have been properly removed giv entirely uniform solutions.

Example II 40 grams of chopped safety film support such as is employed in the preceding example except that it contained no dye as in the first example was stirred and heated to -212 F. in about 800 cc. of a solution. of 0.25 per cent KMI104 and 0.5 per cent H2804 in water. The treatment was continued until the permanganate color wa gone. The MnOz was removed by stirring with two warm acidified aqueous solutions of sodium acid sulfite of 2.5 per cent concentration in water. The scrap was then rinsed and dried as in th preceding example. The product when dissolved in the solvent mixture used in Example I gave a solution which Was clear, colorless, and free of grain.

It may be seen from the above examples that under the conditions described th potassium. permanganate in the treating liquor need be only about /4 per cent concentration unless there is some reason why the permanganate will be used up. For instance, in the first example using a colored film, permanganate was necessary to oxidize the color present therein. The amount of permanganate may be selected by the individual operator for the conditions employed. For instance, with some kinds of dye a 1 per cent concentration of potassium permanganate is sufficient while with other kinds of dye even the use of a treating liquor having a 2 per cent permanganate concentration may not be sufiicient to completely discharge the color. In some kinds ofphotographic film more than one type of dye may be employed or a heavier coating of dye material may be used. In those cases the amount of; potassium permanganate employed would obviously be adjusted to provide for removal of the dye as well as the subbing layers.

For the treatment of film scrap by our invention, the removal of any gelatin layers such as of emulsion is ordinarily desirable. This may be accomplished by thoroughly washing the scrap with hot water before subjecting it to the permanganate treatment.

We claim:

1. A method of separating a thin layer of a lower fatty acid ester of cellulose from a thicker layer of a lower fatty acid ester of cellulosev to which it adheres in which the cellulose ester which comprises the thin layer has an acyl content of at least 5 per cent less than the cellu- .ester of cellulose which comprises first washing lose ester of the thicker layer which comprises treating the material at a temperature of at least 150 F. but not more than the boiling temperature of the liquid employed under conditions of operation with an aqueous solution of an alkali metal permanganate and an inert strong acid in sufiicient amount to remove the thin layer from the thicker layer.

2. A method of separating a thin layer of a lower fatty acid ester of cellulose from a thicker layer of a lower fatty acid ester of cellulose to which it adheres in which the cellulose ester which comprises the thin layer has an acyl content of at least per cent less than the cellulose ester of the thicker layer which comprises treating the material at a temperature of at least 150 F. but not more than the boiling temperature of the liquid employed under conditions of operation with an aqueous solution of potassium permanganate and an inert strong acid in sufficient H amount to remove the thin layer from the thicker layer.

3. A method of recovering cellulose organic ester film base material from photographic film scrap containing it which comprises first washing the scrap with hot water to remove gelatinous material therefrom, treating the so-washed material at a temperature of at least 150 F. but not more than the boiling temperature of the liquid employed under conditions of operation with an aqueous solution of an alkali metal permanganate and an inert strong acid for a suf ficient time to remove subbing or other layers which are present upon the film base.

4. A method of separating a thin layer of a lower fatty acid ester of cellulose from a thicker layer oi a lower fatty acid ester of cellulose to which it adheres in which the cellulose ester which comprises the thin layer has an acyl content of at least 5% less than the cellulose ester of the thicker layer, which comprises treating the material at a temperature of at least 150 F. but not more than the boiling temperatur of the liquid employed under conditions of operation with an aqueous solution of an alkali metal per manganate and sulfuric acid, the permanganate being present in suflicient amount to remove the thin layer from the thicker layer.

5. A method of recovering the film base from photographic film scrap having a base of a lower fatty acid ester of cellulose and a subbing layer thereon of a farther hydrolyzed lower fatty acid the film scrap with hot water to remove the gelatinous material therefrom and treating the sowashed material with an aqueous solution of an alkali metal permanganate and sulfuric acid at a temperature of at least F. but not more than the boiling temperature of th liquid employed under conditions of operation, the permanganate being present in suflioient amount to remove the thin layer from the thicker layer.

6. A method of separating a thin layer of a lower fatty acid ester of cellulose from a thicker layer of a lower fatty acid ester of cellulose to which it adheres in which the cellulose ester, which comprises the thin layer, has an acyl content of at least 5% less than the cellulose ester of the thicker layer, which comprises treating the material at a temperature of ISO-212 F. with an aqueous solution of an alkali metal permanganate and an inert strong acid in a sufiicient amount to remove the thin layer from the thicker layer.

7. A method of separating a thin layer of a lower fatty acid ester of cellulose from a thicker layer of a lower fatty acid ester of cellulose to which it adheres in which the cellulose ester, which comprises the thin layer, has an acyl content of at least 5% less than the cellulose ester of the thicker layer, which comprises treating the material at a temperature of 180-212 F. with an aqueous solution of potassium permanganate and sulfuric acid, the permanganate being present in sufficient amount to remove the thin layer from the thicker layer.

8. A method of recovering the film base ester from photographic film scrap in which the base of the film comprises a cellulose acetate butyrate having an acetyl content of 30% and a butyryl content of 17% and the subbing layer thereon comprises a cellulose acetate propionate containing about 24% acetyl and 15.5% propionyl, which comprises washing the film scrap in hot water to remove the gelatinous material therefrom and subsequently treating the scrap at a temperature of 180-212" F. with an aqueous solution of potassium permanganate and a strong mineral acid, the permanganate being present in sufiicient amount to remove the subbing layer from the film base.

CHARLES R. FORDYCE. JOSEPH GAIL STAMPFLI. 

